A magnetic disk device for magnetically recording and reproducing information is a high-precision device in which, to perform recording or reproduction of information, a slider on which a magnetic head is mounted is floated above a recording/reproduction surface of a magnetic disk which is a recording medium, with a spacing maintained generally constantly therebetween. The slider is attached to a distal end of an actuator arm of the magnetic disk device. The slider incorporates a magnetic head for performing at least one of recording and reproduction of information. Ordinarily, the magnetic head is placed in an air lubrication surface of the slider in the vicinity of an air-flow-out end thereof, which opposes the magnetic disk. An air flow generated with the rotation of the magnetic disk is drawn into the space between the air lubrication surface and the magnetic disk surface, thereby floating the slider from the magnetic disk.
The slider thus floats above the rotating magnetic disk. The floating altitude corresponds to the thickness of the air lubrication film, i.e., the distance between the magnetic disk surface and the slider. Thus, the surface of the slider facing the magnetic disk forms an air lubrication surface to form and maintain self-pressurizing air lubrication film between the slider and the magnetic disk. This film ensures that the slider and the magnetic disk do not easily contact each other during rotation of the magnetic disk, and that friction and wear are limited.
In recent years, the data recording density of magnetic disk devices has been remarkably increased. It is said that the rate of increase in recording density is 100% per year. This remarkable increase in recording density has been achieved by use of a GMR head having improved high-density reproduction characteristics and by reducing the track pitch of recording tracks in the magnetic disk surface. However, it is also necessary to simultaneously reduce the amount of floating of the slider in which a magnetic head is mounted from the magnetic disk. The amount of floating is presently reduced to an extremely small value of about 10 nm. There is a demand for further reducing the amount of floating, and the importance of evaluations of mechanical characteristics and tribological characteristics of magnetic disks for assurance of the reliability of devices is increasing.
Various inspection devices have been used to make such evaluations. One of them is a device for inspection of contact between a slider and a magnetic disk. For example, techniques and so on disclosed in Japanese Patent Publication No. 6-40065 and Japanese Patent Laid-Open No. 8-297816 are known as a contact inspection device of this kind.
FIG. 12 shows an example of a device conventionally used for inspection of contact between a slider and a magnetic disk. In FIG. 12, reference numeral 1 denotes a magnetic disk which is a recording medium; reference numeral 2 a slider on which a magnetic head (not shown) for performing signal recording/reproduction on or from the magnetic disk 1; reference numeral 3 a spindle which is a rotating and holding mechanism which rotates the magnetic disk 1 while holding the magnetic disk 1; reference numeral 7 a spindle drive circuit which drives the spindle 3; reference numeral 6 an arm which supports the slider 2; reference numeral 5 a voice coil motor which drives the arm 6; and reference numeral 8 an actuator drive circuit which drives the voice coil motor 5.
The magnetic disk 1 is fixed on the spindle 3, for example, by screw fastening or the like. The slider 2 is made of a ceramic material typified by Al2O3—TiC for example. An air lubrication surface, not shown in the figure, is formed in a surface of the slider 2 facing the magnetic disk 1 by machining, etching, or the like.
The arm 6 is capable of springy action in the direction of pressing toward the magnetic disk 1. The air lubrication surface of the slider 2 is pressed against the recording/reproduction surface of the magnetic disk 1 with a constant load of, for example, 20 mN. The arm 6 is attached to the voice coil motor 5 and rotates on the shaft of the voice coil motor 5 through a certain range of 30 degrees for example. With the rotation of the voice coil motor 5, the arm 6 swings generally parallel to the recording/reproduction surface of the magnetic disk 1. With this action, the slider 2 moves generally in a radial direction of the magnetic disk 1.
An AE sensor 12 provided as a vibration detecting element is mounted on the arm 6. The AE sensor 12 is constituted by a piezoelectric element (PZT) for example. The AE sensor 12 detects acoustic elastic waves (acoustic emission, hereinafter referred to as AE) and outputs corresponding electrical signals.
Reference numerals 20 denotes a wide-band amplifier which amplifies the signal output from the AE sensor 12; reference numerals 30 a filter circuit which extracts frequency components necessary for contact inspection from a signal output from the wide-band amplifier 20; and reference numerals 50 an oscilloscope which displays a signal output from the filter circuit 30.
The operation of this contact inspection device will be described. This kind of conventional inspection device was devised to inspect the condition of contact between the slider 2 and the magnetic disk 1 of a magnetic disk device using a start/stop system called a CSS (contact start/stop) system. When the spindle 3 is stopped, the magnetic disk 1 is in contact with the slider 2. The slider 2 has the air lubrication surface in the face facing the recording/reproduction surface of the magnetic disk 1. When the spindle 3 starts rotating, the slider 2 starts gradually floating by drawing an air flow generated with the rotation of the magnetic disk 1 into the space between the slider 2 and the magnetic disk 1.
The voice coil motor 5 moves the arm 6 to move the slider 2 to a predetermined position generally in a radial direction of the magnetic disk 1. When the spindle 3 enters a state of rotating at a high constant speed (e.g., 5400 rpm), the slider 2 floats while generally constantly maintaining a spacing between the slider 2 and the magnetic disk 1 by maintaining the self-pressurizing air lubrication film formed between the slider 2 and the magnetic disk 1. When the spindle 3 is stopped, the slider 2 again contacts the magnetic disk 1. Thus, the magnetic disk 1 contacts the slider 2 when stopped, and the slider 2 is floated during rotation of the magnetic disk 1 to maintain the magnetic disk 1 and the slider 2 in a non-contact state.
In spindle 3 rotation starting and stopping processes, the slider 2 and the magnetic disk 1 contact and slide on each other. With this contact and sliding, AE is generated. This AE is detected by the AE sensor 12. Even when the magnetic disk 1 is rotating, attachment of dust to the slider 2 or configurational defect of the magnetic disk 1 may cause contact between the slider 2 and the magnetic disk 1, which is accompanied by generation of AE. This AE is detected by the AE sensor 12.
The voltage of the detection signal from the AE sensor 12 at this time is very low, several microvolts to several hundred microvolts. However, the detection signal includes information relating to the contact caused between the slider 2 and the magnetic disk 1.
The detection output from the AE sensor 12 is amplified by the wide-band amplifier 20 to an observable level (e.g., 40 to 60 dB), noise components are then removed from the amplified detection output by the filter circuit 30, and the resultant signal is displayed on the oscilloscope 50.
Characteristics of the contact including the strength and duration are evaluated on the basis of the results of observation of the waveform of the output signal from the AE sensor 12 displayed on the oscilloscope 50.
The contact inspection device presently used generally has been described. In the case where the AE sensor 12 is mounted on the arm 6, however, not only AE generated by the contact between the slider 2 and the magnetic disk 1 but also vibrations of the arm 6 and the slider 2 are simultaneously detected by the AE sensor 12. A contact inspection device has therefore been devised as disclosed in Japanese Patent Laid-Open No. 2000-173032, which uses, as a method of measuring the condition of contact between the slider 2 and the magnetic disk 1 more accurately, an arrangement in which the AE sensor 12 is mounted on the magnetic disk 1 side and the detection signal from the AE sensor 12 is transmitted to the wide-band amplifier 20 through a slip ring, thereby preventing the detection of vibration of the arm 6 or slider 2 by the AE sensor 12. In Japanese Patent Laid-Open No. 2000-173032, the possibility of transmission by means of a rotary transformer of the detection signal from the AE sensor 12 mounted on the magnetic disk side is proposed.
A method of transmitting the detection signal by using the rotary transformer disclosed in Japanese Patent Laid-Open No. 2000-173032 will be described with reference to FIGS. 13 and 14.
FIG. 13 is a block diagram of a contact inspection device constructed by using a rotary transformer, and FIG. 14 is a sectional view of spindle 3 used in the contact inspection device shown in FIG. 13.
In FIG. 14, reference character 3a denotes a rotor having a shaft 3c. The shaft 3c is rotatably supported by a radial bearing 3d fixed on a stator 3b. 
Reference characters 3g and 3f respectively denote rotary transformers placed so as to respectively face an outer surface of the radial bearing 3d and the rotor 3a. Reference characters 3n and 3m connection terminals on the primary and secondary sides of the rotary transformers 3g and 3f. Reference character 3h denotes an annular permanent magnet attached to the rotor 3a. Reference character 3i denotes a coil fixed to the stator 3b and facing the permanent magnet 3h. The permanent magnet 3h and the coil 3i constitute a motor.
A fluid bearing construction is provided which includes grooves formed in the shaft 3c and the thrust bearing 3e and a bearing portion filled with oil. Dynamic pressure of oil produced by rotation maintains a non-contact condition between the shaft 3c and the radial bearing 3d and between the shaft 3c and the thrust bearing 3e. 
The spindle 3 shown in FIG. 14 has a fluid bearing structure, as described above, and is therefore free from occurrence of sliding between the rotor and the stator with the rotation of the spindle 3, unlike contact-type bearings using a ball bearing or the like. Also, an electrical signal can be extracted from the rotor 3a side to the outside of the rotating body in a non-contact manner by means of the rotary transformers 3g and 3f. 
Accordingly, in use of the thus constructed spindle 3, the output terminal of the AE sensor 12 mounted on the magnetic disk side 1 is connected to the connection terminal 3m on the primary side of the rotary transformer 3f (see the arrow to 3f′), while the connection terminal 3n on the secondary side of the rotary transformer 3g is connected to the input terminal of the wide-band amplifier 20 as indicated by arrow 3g′, thus enabling the detection signal from the AE sensor 12 to be extracted to an external measuring circuit system in a non-contact manner.
This arrangement is free from the risk of mechanical noise generated by slide contact between the slip ring and brushes from being superimposed on the detection signal from the AE sensor 12, and therefore offers the advantage of ensuring a further improvement in accuracy.
Among start/stop systems for magnetic disk devices in recent years, the system in which the slider 2 is directly loaded on the magnetic disk surface 1 and directly unloaded from the magnetic disk surface, i.e., the so-called ramp load system, is becoming prevalent. There is a demand for grasping the condition of contact between the magnetic disk 1 and the slider 2 in the direct loading and direct unloading processes.
However, vibration of the arm 6 or the slider 2 occurs during direct loading and direct unloading since direct loading and direct unloading are accompanied by turning of the arm 6. It is extremely difficult to evaluate contact between the slider 2 and the magnetic disk 1 by using the contact inspection device having the AE sensor 12 mounted on the arm 6 and presently used generally.
Also, the strength of AE accompanying contact between the slider 2 and the magnetic disk 1 in the direct loading and direct unloading processes in the ramp load system are one severalth to one several tenth of that in the case of the CSS system, and the duration of AE in the same situation is markedly short, about 1 ms. Therefore there is a need to measure the output voltage and time response with extremely high accuracy even if the AE sensor 12 is mounted on the magnetic disk side. In doing so with the slip ring transmission system, the detection signal cannot be accurately captured because the influence of slide noise generated between the slip ring and brushes is large. Also, piezoelectric elements typified by the AE sensor 12 ordinarily have a considerably high internal impedance and an optimum transmission system design is required for transmission from such a sensor even in the case where the rotary transformer is used.
In the direct unloading process, the air lubrication film formed between the slider 2 and the disk 1 is scraped off, so that a so-called squeeze force acts on the slider 2 in the magnetic disk 1 direction. There are two of contact between the slider 2 and the magnetic disk 1 in the direct unloading process: a first mode in which the slider 2 and the magnetic disk 1 are brought into contact with each other by the action of the squeeze force in the process of scraping off the air lubrication film; and a second mode in which after scraping off of the air lubrication film the arm 6 on which the slider 2 vibrates as a result of scraping off of the air lubrication film and the vibration of the arm 6 causes the slider 2 to contact the magnetic disk 1. In the conventional art, however, these two modes cannot be evaluated separately from each other.
The present invention has been achieved in consideration of these problems, and an object of the present invention is to optimize the characteristics of an electrical circuit including a rotary transformer and an AE sensor 12 in the contact inspection method and device having the AE sensor 12 mounted on the rotating body side, i.e., the magnetic disk 1 side, and to thereby implement measurement of contact between the slider 2 and the magnetic disk 1 with higher accuracy in comparison with the conventional art. Another object of the present invention is to identify modes of contact between the slider 2 and the magnetic disk 1 in the direct unloading process and to enable the mode to be evaluated separately from each other. In the present invention, a proposition is made to identify modes of contact between the slider 2 and the magnetic disk 1 in the direct unloading process and to separately evaluate the modes while using the method of mounting the AE sensor on the magnetic disk 1 side.